1. Field of the Invention
The present invention relates to a disc brake assembly for automotive vehicles, and more particularly to a disc brake assembly equipped with a parking brake mechanism, wherein a piston is axially slidably disposed through a sealing ring within a cylinder body of a caliper member to be actuated by hydraulic fluid under pressure supplied into the cylinder body or operation of the parking brake mechanism.
2. Description of the Prior Art
Such a conventional disc brake assembly as described above has been proposed in Japanese Patent Publication No. 51-19556, wherein the parking brake mechanism includes a cup-shaped piston axially slidable within a cylinder body of a caliper member, an adjusting bolt arranged coaxially within the piston and secured to the same, an adjusting nut threadedly coupled over the adjusting bolt and engaged with an internal end wall of the cylinder body through a first thrust bearing, a cup-shaped retainer member disposed within the piston to contain the adjusting bolt and nut and fixed to the internal wall of the piston, a coil spring arranged in surrounding relationship with the adjusting nut and engaged at one end thereof with the retainer member to bias the adjusting nut toward the internal end wall of the cylinder body, a second thrust bearing interposed between the other end of the coil spring and an annular shoulder of the adjusting nut, a plunger axially slidably disposed within a bore formed in a bottom wall of the cylinder body coaxially with the piston and being opposed to the adjusting nut with a predetermined clearance, a cam shaft rotatably mounted within a lateral bore formed in the bottom wall of the cylinder body and being formed with a cam groove facing the rear end of the plunger, and a toggle engaged at one end thereof with the rear end of the plunger and at the other end thereof with the cam groove.
In operation of the parking brake mechanism described above, the piston is moved forward by hydraulic fluid under pressure supplied into the cylinder body to cause forward movement of the adjusting bolt therewith. In this instance, the second thrust bearing cooperates with the coil spring to permit rotation of the adjusting nut in accordance with the forward movement of the adjusting bolt so as to effect automatic adjustment of clearances of the brake shoes with respect to the rotary brake disc in the disc brake assembly. When the piston is pushed into the cylinder body for replacement of the brake shoes, the adjusting bolt is threaded into the adjusting nut to rotate it on the first thrust bearing. Thus, the replacement of the brake shoes is carried out without causing rotation of the piston.
In manufacturing process of the disc brake assembly, however, the adjusting bolt must be secured to the piston, and the toggle, the plunger, the first thrust bearing, the adjusting nut, the second thrust bearing, the coil spring and the retainer member each must be successively assembled within the small cylindrical bores in the cylinder body. This results in decrease of efficiency in assembling work of the components.